JP2019012143A - Fixing device - Google Patents

Abstract

To solve the problem in which when the printing speed becomes higher in the future, there is a possibility that the timing of increasing a heat generation amount of a heater is delayed with respect to the timing of temperature drop in a film deteriorating, and countermeasures such as always supplying a larger amount of power to the heater in anticipation of the temperature drop in the film so that fixation failure does not occur are necessary at that time, thus deteriorating energy saving performance.SOLUTION: A fixing device includes: a cylindrical film; a heater coming into contact with an inner surface of the film on a first surface; and a heat conduction member in contact with a second surface of the heater. The heat conduction member has an extension part extending in a direction toward the first surface from the second surface of the heater further on the outer side than an end part of the heater in a rotation direction of the film and coming into contact with the inner surface of the film, and a temperature detection member provided so as to come into contact with the heat conduction member. A control part controls power supplied to the heater so that the temperature of the temperature detection member becomes a target temperature.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a fixing device used in an image forming apparatus such as an electrophotographic copying machine or a laser printer.

  The following configuration is known as a fixing device used in an electrophotographic image forming apparatus. It is the structure which has a cylindrical film, the heater which contacts a film, and the pressurization roller which forms a nip part with a heater through a film. The recording material carrying the unfixed toner image is heated while being conveyed at the nip portion, and the toner image is fixed on the recording material. Since this fixing device uses a film having a small heat capacity, it is characterized by a short warm-up time and low power consumption.

  By the way, in the fixing device of Patent Document 1, the temperature detection member is provided so as to contact the heater. The electric power supplied to the heater is controlled so that the temperature detected by the temperature detection member becomes a target temperature at which the fixing process can be performed. Since this structure can detect the temperature change of the heater which is a heat source with high responsiveness by the temperature detection member, it is highly safe.

JP 2017-97224

  However, the configuration of Patent Document 1 is disadvantageous in that the time until the temperature change of the film is detected by the temperature detection member tends to be long. This is because the heater is interposed in the heat transfer path from the film to the temperature detection member. If the printing speed is increased in the future, the timing for increasing the amount of heat generated by the heater may be delayed with respect to the timing when the film temperature decreases. At that time, it is necessary to take measures such as always supplying a large amount of electric power to the heater in anticipation of a temperature drop of the film so that fixing failure does not occur, and energy saving performance is reduced.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device that can detect a temperature change of a film with high responsiveness by a temperature detection member.

  A preferred embodiment for solving the above problems is a plate-like heater having a rotatable cylindrical film, a first surface, and a second surface opposite to the first surface. The first surface is in contact with the inner surface of the film, the heat conductive member is long in the longitudinal direction of the heater and is in contact with the second surface of the heater, and is supplied to the heater And a control unit that controls electric power, wherein the heat conduction member is a rotation of the film, wherein the heat conduction member heats the toner image with the heat of the heater via the film and fixes the toner image on the recording material. An extension portion extending in a direction from the second surface of the heater toward the first surface outside the end portion of the heater in a direction and contacting the inner surface of the film, and contacting the heat conducting member The temperature detection member provided to And, wherein the control unit is characterized in that the temperature of the temperature sensing member to control the power supplied to the heater so that the target temperature.

  It is possible to provide a fixing device that can detect a temperature change of the film with high responsiveness by the temperature detection member.

1 is a schematic cross-sectional view of an image forming apparatus including a fixing device according to Embodiment 1. FIG. 1 is a schematic cross-sectional view of a fixing device according to Embodiment 1. FIG. 1 is a schematic cross-sectional view of a heater according to Example 1. FIG. 2 is an enlarged cross-sectional view showing a positional relationship among a fixing film, a heater, a high heat conduction member, and the like according to Example 1. FIG. 2 is a perspective view of a heater and a heater holder according to Embodiment 1. FIG. 6 is an enlarged cross-sectional view showing a positional relationship among a fixing film, a heater, a high heat conductive member, and the like according to a modification of Example 1. FIG. 6 is an enlarged cross-sectional view illustrating a positional relationship among a fixing film, a heater, a high heat conduction member, and the like according to Example 2. 6 is an enlarged cross-sectional view showing a positional relationship among a fixing film, a heater, a high heat conductive member, and the like according to a modification of Example 2.

[Example 1]
A fixing device according to a first embodiment of the present invention will be described below with reference to the drawings. First, the overall configuration of the image forming apparatus in this embodiment will be described, and then the fixing device will be described.

(Image forming device main unit)
In this embodiment, an example of a method for forming an unfixed toner image on a recording material and an example of an image forming apparatus will be described with reference to a schematic diagram shown in FIG. The image forming apparatus 50 in this embodiment is an electrophotographic image forming apparatus that directly transfers a toner image on a photosensitive drum onto a recording material P. On the peripheral surface of the photosensitive drum 1 as an image carrier, the charger 2, the exposure device 3 for irradiating the photosensitive drum 1 with the laser light L, the developing device 5, and the transfer roller in order along the rotation direction (arrow R1 direction). 10 and a photosensitive drum cleaner 16 are arranged. First, the surface of the photosensitive drum 1 is charged to a negative polarity by the charger 2. Next, an electrostatic latent image is formed on the surface of the charged photosensitive drum 1 by the laser beam L of the exposure means 3 (the surface potential of the exposed portion is increased). The toner of this embodiment is charged with a negative polarity, and the developing device 5 containing black toner attaches the negative toner only to the electrostatic latent image portion on the photosensitive drum 1, and the toner image is formed on the photosensitive drum 1. It is formed. When the recording material P is fed by the paper feed roller 4, the recording material P is transported to the transfer nip N by the transport roller 6. A positive-polarity transfer bias that is opposite to the polarity of the toner is applied to the transfer roller 10 from a power source (not shown), and the toner image on the photosensitive drum 1 is transferred onto the recording material P at the transfer nip N. The The transfer residual toner on the surface of the photosensitive drum 1 after the transfer is removed by a photosensitive drum cleaner 16 having an elastic blade. The recording material P carrying the toner image is conveyed to the fixing device 100, where the toner image on the surface is heated and fixed.

(Fixing device)
The fixing device 100 of this embodiment will be described below. FIG. 2 is a cross-sectional view of the fixing device 100 in this embodiment. The fixing device 100 includes a fixing film 112, a heater 113, a heater holder 130, a pressure roller 110, and a heat conduction member 140.

  The heater 113 contacts the inner surface of the fixing film 112 and heats the fixing film 112. The pressure roller 110 forms a nip portion N together with the heater 113 via the fixing film 112. When the pressure roller 110 is driven in the direction of arrow R1 in the drawing, the fixing film 112 receives frictional force from the pressure roller 110 at the nip portion N and rotates in the direction of arrow R2. When the recording material P to which the unfixed toner image T has been transferred is conveyed from the direction of arrow A1 to the nip portion N in the drawing, the toner image T is heated and fixed to the recording material.

  The fixing film 112 will be described. The fixing film 112 is configured to be rotatable, and is a cylindrical member having an outer diameter of φ18 mm when no external force is applied. The fixing film 112 has a multilayer structure in the thickness direction. The fixing film 112 has a base layer (not shown) and a release layer (not shown) formed outside the base layer. In consideration of heat resistance and rigidity, the base layer is made of a metal such as stainless steel or nickel, or a heat resistant resin such as polyimide. In this example, a polyimide resin was used as the material for the base layer of the fixing film 112, and a carbon-based filler was added to improve the thermal conductivity and strength. The thinner the base layer is, the easier it is to transfer the heat of the heater 113 to the surface of the fixing roller 110, but the strength is reduced. Therefore, the thickness is preferably about 15 μm to 100 μm. The release layer is preferably made of a fluororesin such as perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene resin (FEP). In this example, among the fluororesins, PFA having excellent releasability and heat resistance was used. The release layer may be a tube-coated one or a surface coated with a paint. In this example, the release layer was molded by a coating excellent in thin-wall molding. The thinner the release layer is, the easier it is to transfer the heat of the heater 113 to the surface of the fixing film 112. However, if the release layer is too thin, the durability deteriorates, so about 5 to 30 μm is preferable. Although not used in this embodiment, an elastic layer may be provided between the base layer and the release layer. In that case, as the material of the elastic layer, silicone rubber, fluorine rubber, or the like is used.

  The pressure roller 110 will be described. The outer diameter of the pressure roller 110 is φ20 mm, and an elastic layer 116 having a thickness of 4 mm and an iron cored bar 117 of φ12 mm is formed. As a material of the elastic layer 116, solid rubber or foamed rubber is used. Foamed rubber has a low heat capacity, low thermal conductivity, and heat on the surface of the pressure roller 110 is difficult to be absorbed into the inside, so that there is an advantage that the surface temperature is likely to rise and the rise time can be shortened. In this example, foamed rubber obtained by foaming silicone rubber was used. If the outer diameter of the pressure roller 110 is smaller, the heat capacity can be suppressed. However, if the pressure roller 110 is too small, the width of the nip portion N becomes narrower, so an appropriate diameter is required. In this embodiment, the outer diameter is set to φ20 mm. . Regarding the thickness of the elastic layer 116, if it is too thin, heat escapes to the metal core, so that an appropriate thickness is necessary. In this embodiment, the thickness of the elastic layer 116 is 4 mm. A release layer 118 made of PFA is formed on the elastic layer 116 as a toner release layer. Like the release layer of the fixing film 112, the release layer 118 may be a tube coated or a surface coated with a paint, but in this embodiment, a tube having excellent durability was used. As a material for the release layer 118, in addition to PFA, a fluororesin such as PTFE or FEP, a fluororubber having good releasability, a silicone rubber, or the like may be used.

  The heater 113 will be described. FIG. 3 is a schematic cross-sectional view perpendicular to the longitudinal direction of the heater 113. The heater 113 is a long and thin plate-like member having a first surface 113a that contacts the inner surface of the fixing film 112 and a second surface 113b that is the surface opposite to the first surface 113a. The heater 113 includes a substrate 1130, a heating resistor 1131 provided on the substrate 1130, and a protective layer 1132 provided to cover the heating resistor 1131. The substrate 1130 is formed of a ceramic such as alumina or aluminum nitride. The substrate 1130 of this embodiment is made of alumina and has a width of 6 mm and a thickness of 1 mm in the recording material conveyance direction. The heating resistor 1131 is formed by applying 10 μm of Ag / Pd (silver palladium) to the surface of the substrate 1130 by screen printing. The protective layer 1132 is made of glass having a thickness of 50 μm.

  The heater holder 130 will be described. The heater holder 130 is a support member that supports the second surface 113 b of the heater 113. The heater holder 130 is formed of a liquid crystal polymer that is a heat-resistant resin.

  The heat conductive member 140 will be described. FIG. 4 is a cross-sectional view perpendicular to the longitudinal direction of the heater 113, and is an enlarged cross-sectional view showing the positional relationship of the fixing film 112, the heater 113, the high heat conductive member 140, and the like. The heat conducting member 140 is provided so as to contact the second surface 113 b of the heater 113 and be sandwiched between the heater 113 and the heater holder 130. A portion having a surface in contact with the second surface 113b of the heater 113 of the heat conducting member 140 is referred to as a heater contact portion 140a. The heater contact portion 140a may be in contact with any surface of the heater 113, but in this embodiment, the heater contact portion 140a is configured to be in contact with the second surface 113b of the heater 113. This is because the heat conducting member 140 can come into contact with the heater 113 over a wide area, and good adhesion can be obtained by receiving the pressure from the pressure roller 110. The heat conducting member 140 has an extension portion 140b outside the upstream end portion of the heater 113 with respect to the rotation direction of the fixing film 112 (recording material conveyance direction). The extension 140b extends in a direction from the second surface 113b of the heater 113 toward the first surface 113a. The extension 140b further extends from the second surface 113b of the heater 113 toward the first surface 113a in a direction away from the heater 113 with respect to the rotation direction of the film, and extends from the inner surface of the fixing film 112. The contact area is wide.

  The material of the heat conducting member 140 may be any material having a higher thermal conductivity than the substrate 1130 of the heater 113. In this embodiment, an aluminum alloy having a thermal conductivity of about 140 W / m · K is used. The heat conductivity of the heat conducting member 140 is preferably 100 W / m · K or more. In a cross section perpendicular to the longitudinal direction of the heater 113, if a line extending the first surface 113a of the heater 113 to the upstream side in the recording material conveyance direction is S1, the extended portion 140b extends to S1.

  FIG. 5 is a perspective view of the heat conducting member 140 and the heater holder 130 according to the present embodiment. The heat conducting member 140 is a member that is long along the longitudinal direction of the heater 113. The extension 140 b is preferably provided in a region of the heat conducting member that overlaps the detection region of the thermistor 115 in the longitudinal direction of the heater 113. The extension 140b of the present embodiment is provided over the longitudinal direction of the heat conducting member 140. Further, the heat conducting member 140 is in contact with the heater 113 across the small size recording material sheet passing region and the non-sheet passing region, and also has an effect of suppressing the temperature increase of the non-sheet passing part.

  Next, the thermistor 115 as a temperature detection member shown in FIGS. The thermistor 115 is provided so as to come into contact with a surface of the heater contact portion 140a of the heat conducting member 140 that is opposite to the surface that contacts the second surface 113b of the heater 113. The control unit 1000 shown in FIG. 2 controls the electric power supplied to the heater 113 by controlling the triac 1001 so that the temperature detected by the thermistor 115 becomes a target temperature that can be fixed.

  Next, detailed problems and effects of the present invention will be described. When the recording material reaches the nip portion N, it takes heat away from the fixing film 112 in the vicinity of the nip portion N. The thermistor 115 detects the temperature change of the fixing film 112 deprived of heat by the recording material, and the control unit 1000 controls the power supplied to the heating resistor 1131 of the heater 113 so that the detected temperature becomes the target temperature. To do. At this time, when a pattern having a high printing rate such as a graphic image or a recording material having a high water content is fixed, the recording material takes more heat from the fixing film 112 in the vicinity of the nip portion. Decrease significantly. At this time, if the time until the thermistor 115 detects the temperature drop of the fixing film 112 becomes longer, the timing of increasing the amount of heat generated by the heater 113 is delayed and the temperature of the fixing film 112 continues to fall. If the fixing film 112 is left as it is, fixing failure occurs. Therefore, when fixing processing is performed on a pattern having a high printing rate or a recording material having a high moisture content, the heater 113 is provided in advance so that the fixing property can be satisfied even if the temperature of the fixing film 112 is greatly reduced. A method of always setting the target temperature of the battery to a higher value is conceivable. However, the target temperature of the temperature detection member 115 is always set to a high value, which means that excessive power is required even in the case of a recording material on which a low-print image that does not require much heat for fixing is formed. Therefore, there is a problem that energy saving performance is lowered.

  Therefore, in this embodiment, as a heat transfer path from the fixing film 112 to the thermistor 115, not only a path through the two parts of the heater 113 and the heat conduction member 140 but also a path through only the heat conduction member is provided. Yes. Accordingly, even if the thermistor 115 is not in direct contact with the fixing film 112, the thermistor 115 can detect the temperature change of the fixing film 112 through the heat conducting member 140 with high responsiveness.

  In this embodiment, the extended portion 140b of the heat conducting member 140 is provided only on the upstream side of the heater 112 in the rotation direction of the fixing film 112, but is not limited thereto. The extension 140 b of the heat conducting member 140 may be provided only on the downstream side of the heater 112 in the rotation direction of the fixing film 112.

  Next, a modification of the present embodiment will be described. FIG. 6 is an enlarged cross-sectional view showing the positional relationship among the fixing film 112, the heater 113, the high heat conductive member 140, and the like of the fixing device of this modification. The heat conducting member 140 includes an upstream extension on the upstream side of the heater 112 in the rotation direction of the fixing film 112 and a downstream extension 140 b on the downstream side. In the configuration of the modified example, the contact area between the extension 140 b of the heat conducting member 140 and the fixing film 112 is wider than that in the first embodiment. Therefore, the thermistor 115 can detect the temperature change of the fixing film 112 through the heat conducting member 140 with higher responsiveness.

[Example 2]
The fixing device of the present embodiment is different from the first embodiment only in the configuration of the heat conduction member, and the other components are the same. Therefore, the configuration other than the heat conducting member is omitted. FIG. 7 is an enlarged cross-sectional view showing the positional relationship between the fixing film 112, the heater 113, the high heat conductive member 140, and the like of this embodiment.

  As shown in FIG. 7, the feature of this embodiment is a configuration in which the extended portion 140 b of the heat conducting member 140 protrudes in the a direction (fixing film 112 side) from the first surface 113 a of the heater 113. The a direction is a direction from the second surface 113b toward the first surface 113a.

  Here, the definition of the protrusion amount h of the extension 140b will be described. A line obtained by extending the first surface 113a of the heater 113 to the upstream side in the recording material conveyance direction is denoted by S1, and a line passing through the portion closest to the inner surface of the fixing film 112 of the extension portion 140b of the heat conducting member 140 is parallel to S1. Is S2. When the portion of the extended portion 140b of the heat conducting member 140 closest to the inner surface of the fixing film 112 is on the line S1, the protrusion amount is 0, and the protrusion amount h can be defined as the distance from the line S1 to the line S2.

  By the way, in order for the thermistor 115 to detect the temperature change of the fixing film 112 through the heat conducting member 140 with high responsiveness, the extension 140b of the heat conducting member 140 is in stable contact with the fixing film 112. Is desirable. However, since the fixing film 112 is a possible member, the position of the fixing film 112 in the thickness direction may swing when rotating. At that time, the contact area between the extension 140b of the heat conducting member 140 and the fixing film 112 varies.

  Therefore, in this embodiment, by ensuring the protrusion amount h, the variation in the contact area between the extension 140b of the heat conducting member 140 and the fixing film 112 is reduced. As a result, the thermistor 115 can detect a temperature change of the fixing film 112 with higher responsiveness.

  In order to verify the operational effects of the present embodiment, the target temperature of the temperature detection member 115 required for the fixing process under conditions where the printing rate and moisture content of the recording material are different was calculated. When the target temperature is high, the timing for increasing the amount of heat generated by the heater 113 is later than the timing when the temperature of the fixing film 112 is lowered than when the target temperature is low. That is, the responsiveness of detecting the temperature drop of the fixing film 112 by the temperature detection member 115 is low.

  The comparison object of the present embodiment was made into two forms, a comparative form 1 in which the protrusion amount h is −100 μm and a comparative form 2 in which the protrusion amount h is 0 μm. Moreover, in order to confirm the influence of the contact state of the extension part 140b of the heat conductive member 140 and the fixing film 112, the following three conditions were evaluated. The first condition is that the nip portion has a narrow width due to a low applied pressure at the nip portion N and a high roller hardness (pressurizing force 13 kgf, roller hardness 52 °, nip portion width 5 mm). The second condition is a condition where the width of the nip portion becomes wider (pressure 15 kgf, roller hardness 48 °, nip width 7 mm), contrary to the first. The third condition is that the width of the nip portion N is the median value of the two conditions described above (pressure 14 kgf, roller hardness 50 °, nip width 6 mm).

  The print patterns used for the evaluation are a text pattern with a low toner printing rate and a solid black pattern for printing toner on the entire surface. Regarding the moisture content of the recording material, open paper, which is a recording material immediately after the recording material is opened from the package, and left paper, which is a recording material left for about one week after opening, were used. Since the environment was a high temperature and high humidity environment at a temperature of 30 ° C. and a humidity of 80%, the moisture content of the recording material was about 4% for open paper and about 8% for left paper.

  The above evaluation results will be described. The evaluation result of Comparative Example 1 in which the protrusion amount h was −100 μm was as follows. The target temperature required for fixing the solid black pattern needs to be 15 ° C. higher than the target temperature required for fixing the text pattern. The target temperature required for fixing the standing paper has to be 10 ° C. higher than the target temperature required for fixing the open paper. Further, it was confirmed that every time the width of the nip portion N is reduced by 1 mm, the necessary target temperature needs to be increased by 5 ° C. Therefore, the target temperature for satisfying the fixing property under the above three conditions with the width of the nip portion N in the comparative form 1 being 210 ° C.

  Next, the evaluation results of Comparative Example 2 in which the protrusion amount h was 0 μm were as follows. When the width of the nip portion N was 5 mm and 6 mm, the result was the same as in Comparative Example 1. When the width of the nip portion N is 7 mm, the target temperature required for fixing the solid black pattern needs to be 5 ° C. higher than the target temperature required for fixing the text pattern. Further, the target temperature required for fixing the left-sided paper needs to be 5 ° C. higher than the target temperature required for fixing the open paper. That is, only when the width of the nip portion N is 7 mm, the necessary target temperature is lower than that of the comparative form 1. This is because the width of the heater 113 is narrower than the width of the nip portion N, so that the extended portion 140b of the heat conducting member 140 in the vicinity of the heater 113 and the inner surface of the fixing film 112 are brought into contact with each other by the applied pressure of the nip portion N. It is thought that this is because of the heat transfer performed. As described above, with respect to Comparative Examples 1 and 2, the target temperature that can satisfy the fixability of the solid black pattern and the standing paper under the above three conditions in which the width of the nip portion N is changed was 210 ° C.

  Next, the evaluation results of the configuration of this example were as follows. Under the above three conditions in which the width of the nip portion N is changed, the target temperature necessary for fixing the solid black pattern needs to be 5 ° C. higher than the target temperature for fixing the text pattern. In addition, the target temperature required for fixing the left sheet has to be 5 ° C. higher than the target temperature required for fixing the open paper. In the configuration of this example, the target temperature that can satisfy the fixing property between the solid black pattern and the untreated paper was 195 ° C. under the above three conditions in which the width of the nip portion N was varied. In other words, the configuration of this example was able to lower the target temperature of the temperature detection member 115 during the fixing process than in Comparative Examples 1 and 2. This is considered to be because the contact between the extension 140b and the fixing film 112 is maintained even when the fixing film 112 rotates and the rotation trajectory fluctuates. As a result, the temperature drop of the fixing film 112 was detected by the thermistor 115 with high responsiveness, and the amount of heat generated by the heater 113 could be increased.

  As described above, this embodiment has an effect that the thermistor 115 can detect the temperature change of the fixing film 112 through the heat conducting member 140 with higher responsiveness than the first embodiment.

  In this embodiment, the extended portion 140b of the heat conducting member 140 is provided only on the upstream side of the heater 112 in the rotation direction of the fixing film 112, but is not limited thereto. The extension 140 b of the heat conducting member 140 may be provided only on the downstream side of the heater 112 in the rotation direction of the fixing film 112.

  A modification of this embodiment will be described. FIG. 8 is an enlarged cross-sectional view showing the positional relationship among the fixing film 112, the heater 113, the high heat conductive member 140, and the like of the fixing device of this modification. The heat conducting member 140 has an extension 140 b not only on the upstream side of the heater 112 in the rotation direction of the fixing film 112 but also on the downstream side. In this modification, the extension amount 140b on the downstream side also has a protrusion amount h larger than zero. The protruding amount h of the upstream / downstream extension 140b may be different.

  The configuration of this modification has a larger contact area between the heat conducting member 140 and the fixing film 112 than in the second embodiment. Therefore, the thermistor 115 can detect the temperature change of the fixing film 112 through the heat conducting member 140 with higher responsiveness.

DESCRIPTION OF SYMBOLS 100 Fixing device 110 Pressure roller 112 Fixing film 113 Heater 115 Temperature detection member 140 Thermal conduction member 140b Extension part of thermal conduction member

Claims (5)

A rotatable cylindrical film,
A plate-like heater having a first surface and a second surface opposite to the first surface, wherein the first surface is in contact with the inner surface of the film;
A heat conducting member that is long in the longitudinal direction of the heater and is in contact with the second surface of the heater;
A control unit for controlling power supplied to the heater;
A fixing device that heats a toner image with the heat of the heater via the film and fixes the toner image on a recording material.
The heat conducting member extends in a direction from the second surface of the heater toward the first surface outside the end portion of the heater in the rotation direction of the film, and extends in contact with the inner surface of the film. Have
Having a temperature detecting member provided to contact the heat conducting member;
The fixing device controls the electric power supplied to the heater so that the temperature of the temperature detection member becomes a target temperature.   The extension portion extends in a direction from the second surface of the heater toward the first surface outside the end portion of the heater in the rotation direction of the film, and then the heater in the rotation direction of the film. The fixing device according to claim 1, wherein the fixing device extends in a direction away from the fixing device.   The fixing device according to claim 1, wherein the extension portion protrudes from the first surface of the heater toward the film.   The fixing device according to claim 1, wherein the extension portion is provided on an upstream side of the heater in a rotation direction of the film. When the extension is an upstream extension,
The heat conducting member extends in a direction from the second surface of the heater toward the first surface outside the downstream end of the heater in the rotation direction of the film and contacts the inner surface of the film. The fixing device according to claim 4, further comprising a downstream extension portion.

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